Recently, gaming equipment and so on performs processing such as moving sound image localization positions of sound effect and voice of characters (audio objects) with respect to a listener over time. Patent Literature (PTL) 1 discloses a technique for localizing audio objects to a predetermined position, and application of such a technique allows processing to move the audio object over time. For example, as illustrated in FIG. 9, sound images localized at the right side (or left side) of the listener can be moved to localize at the left side (or right side) of the listener, over time.
In FIG. 9, 650 is a sound image localization filter which localizes sound images to the left side, and is the sound image localization filter manufactured with the technique disclosed in PTL 1, for example. Likewise, 651 is a sound image localization filter which localizes sound images to the right side. 652 is a synthesis unit for moving the sound images from side to side. When moving the sound images to the left, a coefficient α in the synthesis unit 652 is set to 1. With this, output signals of the left-localization sound Image localization filter 650 are output from speakers 603a and 603b as sounds, thereby localizing the sound Images to the left side. When moving the sound Images to the right, the coefficient α in the synthesis unit 652 is set to 0. With this, the output signals of the right-localization sound image localization filter 651 are output from the speakers 603a and 603b as sounds, thereby localizing the sound images to the right side. Furthermore, setting the value of a between 0 and 1 allows moving the sound images from side to side.